The present invention comprises an improvement on the invention disclosed in the co-pending application of Amos and Burns, Ser. No. 136183, filed Mar. 31, 1980 and assigned to the assignee of the present application, now abandoned.
As pointed out in the co-pending application, the operation of farm and construction machinery on hills or inclines is potentially hazardous because such vehicles may be tilted to the point where the critical roll angle of the vehicle is exceeded, causing the vehicle to tip and roll, possible to the injury of the operator. Thus, there is a need for a warning system which will provide an alarm or other indication when the vehicle approaches this critical roll angle, and systems have been devised for operating an indicating or warning device when the machine is tilted either on a hillside or incline to a point where it might tip and begin to roll.
A prior art tilt detecting device which can be used in such prior art systems incorporates a bubble level where the bubble normally allows light from a light source to fall upon a photosensor. As the detecting device is tilted, however, the bubble is shifted to a point where it no longer allows light to travel from the source to the photosensor, and the de-energization of the photosensor can be used to energize an indication device, to give warning that the housing of the tilt detecting device has been tilted too much. The problem with such a device is that tilt responsive switches must operate under wide variations in ambient temperature conditions. Since the bubble is established in a fluid, the fluid expands and contracts as the ambient temperature changes. As this fluid expands and contracts, the bubble also expands and contracts, which results in significant changes in the angles to which this type of tilt responsive device is responsive.
Other forms of prior art tilt detecting devices include pendulums where the pendulum bob forms one contact and the housing of the pendulum tilt detecting device forms the other contact, so that if the device is tilted sufficiently, gravity operates the pendulum until it comes in contact with the housing, thus closing the circuit to an alarm or indicator. A similar type of device uses a ball which rolls in a housing as the housing is tilted until it comes into contact with a flat circular contact within the housing to establish a circuit between the housing and the contact for energizing an alarm or warning device. Both this ball tilt detecting device and the pendulum device require an adequate force between the pendulum or ball and the housing or the contact to guarantee reliable sensing. For small tilt angles, such as 0.5 degrees or less, the ball or the pendulum do not apply adequate force to guarantee a reliable contact. If a damping fluid such as silicone oil is used in the device to damp out vibrations, as is typical with almost all tilt detecting devices, the problem is worse because the surface tension of the oil inhibits low resistance contacts and causes significant mechanical hysteresis or sticking.
In the co-pending application there is provided a housing having a basin with a concave surface on which an opaque ball is free to roll transversely to the optical axis from a light source to a light sensor. When the detector is level the ball blocks light from the source from reaching the sensor, but it unblocks the light when the detector is tilted by more than a predetermined amount. The movement of the ball is damped by a transparent silicone liquid, so that its position relative to the axis is generally proportional to the tilt of the detector in a small angular range, regardless of the direction of the tilt.
Many applications for tilt detectors are such that a greater tilt can be tolerated in one direction rather than in another-greater longitudinally then transversely, for example. Moreover, there is no need for a structure where the ball position is proportional to the tilt at low angles.